The Peloponnesian war was fought from 431 to 404 B.C. It was against the Delian league led by Athens, and the Peloponnesian league led by Sparta. The war was fought because the Greek States who could, and would be the strongest out of all of them. And mainly the Spartans were worried about the Athenians growing and getting more powerful. The war took place after the Persian war, and the States disagreed on what to do after. This led straight to war.
The Significance of this is it changed how Greece functioned. It also left an opening for the King of Macedonia to invade.
Pericles point is that Athens is great. Athens has survived so much and lost so much, and yet it is still strong. The Athenians may have lost the war, but they still have so much dignity and perseverance, they really didn’t lose.